Power transmission apparatus, power reception apparatus, method for controlling wireless power transmission system, and storage medium

ABSTRACT

A wireless power transmission system wirelessly transmits power from a power transmission apparatus to a power reception apparatus. The system performs detection processing using a first detection method for detecting an object different from the power reception apparatus. The system determines whether a predetermined condition related to a state of at least either one of the power transmission apparatus and the power reception apparatus is satisfied. Then, the system performs object detection processing using a second detection method, different from the first detection method, according to a result of the determination regarding whether the predetermined condition is satisfied.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 17/211,597, filed on Mar. 24, 2021, which claims priority fromJapanese Patent Application No. 2020-063780 filed Mar. 31, 2020, whichare hereby incorporated by reference herein in their entireties.

BACKGROUND Field

The present disclosure relates to a wireless power transmissiontechnique.

Description of the Related Art

In recent years, technical development for a wireless power transmissionsystem has been widely performed. Japanese Patent Application Laid-OpenNo. 2017-70074 discusses a foreign object detection method conforming tothe Wireless Power Consortium (WPC) standard. Japanese PatentApplication Laid-Open No. 2015-27172 discusses a foreign objectdetection method in which a power transmission apparatus transmits aforeign object detection signal to a power reception apparatus anddetermines the presence or absence of a foreign object by using an echosignal from the power reception apparatus.

The foreign object detection method (Power Loss method) discussed inJapanese Patent Application Laid-Open No. 2017-70074 detects a foreignobject different from the power reception apparatus, based on the resultof measuring a power loss occurring between the power transmissionapparatus and the power reception apparatus during power transmissionfrom the power transmission apparatus to the power reception apparatus.On the other hand, the foreign object detection method discussed inJapanese Patent Application Laid-Open No. 2015-27172 detects a foreignobject based on the result of measuring the attenuation state of thesignal transmitted by the power transmission apparatus. While there area number of methods for detecting a foreign object in performingwireless power transmission, a method for suitably controlling detectionprocessing when a plurality of methods is available has not yet beenestablished.

SUMMARY

Various embodiments of the present disclosure provide techniques andmechanisms for suitably controlling detection processing when aplurality of methods for detecting an object different from the powerreception apparatus is available in performing wireless powertransmission.

According to various embodiments of the present disclosure, a powertransmission apparatus includes a power transmission unit configured towirelessly transmit power to a power reception apparatus, a firstdetection unit configured to perform detection processing using a firstdetection method for detecting an object different from the powerreception apparatus, based on a power loss related to a powertransmission by the power transmission unit, a determination unitconfigured to determine whether a predetermined condition related to astate of at least either one of the power reception apparatus and thepower transmission apparatus is satisfied, and a second detection unitconfigured to perform detection processing using a second detectionmethod for detecting an object different from the power receptionapparatus based on at least either one of a voltage attenuation stateand a current attenuation state related to the power transmission by thepower transmission unit, according to the determination result by thedetermination unit.

Further features of various embodiments of the present disclosure willbecome apparent from the following description of exemplary embodimentswith reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a configuration of apower transmission apparatus according to one embodiment.

FIG. 2 is a diagram illustrating an example of a configuration of apower reception apparatus according to one embodiment.

FIG. 3 is a block diagram illustrating an example of a functionconfiguration of a control unit of the power transmission apparatusaccording to one embodiment.

FIG. 4 is a diagram illustrating an example of a configuration of awireless power transmission system according to one embodiment.

FIG. 5 is a sequence diagram illustrating an example of processing forperforming the wireless power transmission according to one embodiment.

FIG. 6 is a diagram illustrating foreign object detection based on awaveform attenuation method according to one embodiment.

FIG. 7 is a diagram illustrating a method for performing foreign objectdetection based on a transmission power waveform during powertransmission according to one embodiment.

FIG. 8 is a flowchart illustrating an example of processing in a powertransfer phase of the power transmission apparatus according to oneembodiment.

FIG. 9 is a flowchart illustrating an example of processing in the powertransfer phase of the power reception apparatus according to oneembodiment.

FIG. 10 is a diagram illustrating a method for setting a threshold valuein foreign object detection based on a Power Loss method according toone embodiment.

FIG. 11 is a diagram illustrating a method for setting a threshold valuein the foreign object detection based on the waveform attenuation methodaccording to one embodiment.

DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments will be described in detail below with referenceto the accompanying drawings. Although a plurality of features isdescribed in the exemplary embodiments, not all of the plurality offeatures is indispensable to the present invention, and the plurality offeatures may be combined in different ways from those described herein.In the accompanying drawings, identical or similar components areassigned the same reference numerals.

[Configuration of Wireless Power Transmission System]

FIG. 4 illustrates an example of a configuration of a wireless powertransmission system (wireless recharging system) according to oneembodiment of the present disclosure. The system includes, for example,a power reception apparatus 401 and a power transmission apparatus 402.The configurations of the power reception apparatus 401 and the powertransmission apparatus 402 will be described in detail below withreference to FIGS. 2 and 1 , respectively. In the followingdescriptions, the power reception apparatus 401 may be referred to asthe RX and the power transmission apparatus 402 may be referred to asthe TX. The RX is an electronic apparatus that receives power from theTX to charge the built-in battery. The TX is an electronic apparatusthat wirelessly transmits power to the RX placed on a charging stand 403as a part of the TX. Since the charging stand 403 is a part of the TX,hereinafter, “being placed on the charging stand 403” may be referred toas “being placed on the TX (power transmission apparatus 402)”. A range404 enclosed in dotted lines is a range where the RX can receive powerfrom the TX. The RX and the TX can have a function of executingapplications other than a wireless charging application. A smart phoneis an example of the RX, and an accessory device for charging the smartphone is an example of the TX. The RX and the TX may each be a tabletcomputer, a storage device (such as a hard disk drive and a memorydevice), or an information processing apparatus such as a personalcomputer (PC). For example, the RX and the TX may each be an imagingapparatus (such as a still camera and a video camera), an automobile, arobot, a medical instrument, or a printer.

The present system performs wireless power transmission using anelectromagnetic induction method for wireless charging conforming to theWPC standard. More specifically, the RX and the TX perform the wirelesspower transmission for wireless charging conforming to the WPC standardbetween a power reception antenna 205 of the RX and a power transmissionantenna 105 of the TX. The wireless power transmission method to beapplied to the present system is not limited to a method prescribed inthe WPC standard but may be other methods based on electromagneticinduction, magnetic field resonance, electric field resonance,microwaves, or laser, for example. Although, in the present exemplaryembodiment, the wireless power transmission is used for wirelesscharging, the wireless power transmission may be performed for purposesother than wireless charging.

The WPC standard prescribes the magnitude of power guaranteed to bereceived by the power reception apparatus 401 when the power receptionapparatus 401 receives power from the power transmission apparatus 402,based on a value called guaranteed power (hereinafter referred to as“GP”). The GP indicates a guaranteed power value for an output to theloads of the power reception apparatus 401 (e.g., the charging circuitand the battery) even if the power transmission efficiency between thepower reception antenna 205 and the power transmission antenna 105decreases, for example, by a variation of the positional relationbetween the power reception apparatus 401 and the power transmissionapparatus 402. In an example case where the GP is 5 watts (W), even ifthe power transmission efficiency decreases by a variation of thepositional relation between the power reception antenna 205 and thepower transmission antenna 105, the power transmission apparatus 402controls the power transmission to enable outputting at least 5 W to theloads in the power reception apparatus 401.

If a foreign object different from the power reception apparatus 401 ispresent in the vicinity of the power transmission apparatus 402 when thepower transmission apparatus 402 transmits power to the power receptionapparatus 401, the electromagnetic wave for the power transmission mayaffect the foreign object, and the temperature of the foreign object canrise or the foreign object can be damaged. The WPC standard prescribes amethod for detecting a foreign object on the charging stand 403 of thepower transmission apparatus 402, by the power transmission apparatus402, to prevent a temperature rise and damage to the foreign object dueto suspension of the power transmission. More specifically, the WPCstandard prescribes the Power Loss (power loss) method for detecting aforeign object based on the difference between the transmission powerlevel of power transmitted by the power transmission apparatus 402 andthe reception power level of power received by the power receptionapparatus 401. The WPC standard also prescribes the Q value measurementmethod for detecting a foreign object based on the variation of thequality factor (Q value) of the power transmission antenna 105 (powertransmission coil) of the power transmission apparatus 402. Note thatforeign objects that are detected by the power transmission apparatus402 according to the present exemplary embodiment are not limited toobjects existing on the charging stand 403. The power transmissionapparatus 402 detect a foreign object in the vicinity of the powertransmission apparatus 402 and may be able to detect a foreign objectlocated within a range where the power transmission apparatus 402 canperform the power transmission.

The foreign object detection based on the Power Loss method prescribedby the WPC standard will be described below with reference to FIG. 10 .Referring to FIG. 10 , the horizontal axis represents the transmissionpower level of the power transmitted by the power transmission apparatus402, and the vertical axis represents the reception power level of thepower received by the power reception apparatus 401. A foreign objectrefers to an object, other than the power reception apparatus 401, whichaffects the power transmission from the power transmission apparatus 402to the power reception apparatus 401. Examples of such objects includemetal pieces having conductivity.

The power transmission apparatus 402 transmits power of a firsttransmission power value Pt1 to the power reception apparatus 401. Thepower reception apparatus 401 receives power of a first reception powervalue Pr1 (this state is referred to as the Light Load state). Then, thepower transmission apparatus 402 stores the first transmission powervalue Pt1. The first transmission power value Pt1 and the firstreception power value Pr1 are predetermined minimum transmission powerand minimum reception power, respectively. In this operation, the powerreception apparatus 401 controls the loads to receive minimize power.For example, the power reception apparatus 401 may disconnect the loadsfrom the power reception antenna 205 to prevent the received power beingsupplied to the loads (charging circuit and the battery). Subsequently,the power reception apparatus 401 notifies the power transmissionapparatus 402 of the first reception power value Pr1. Upon reception ofthe first reception power value Pr1 from the power reception apparatus401, the power transmission apparatus 402 calculates the power lossPt1−Pr1 (=Ploss1) between the power transmitted by the powertransmission apparatus 402 and the power received by the power receptionapparatus 401, whereby a calibration point 1000 indicating thecorrespondence between the first transmission power value Pt1 and thefirst reception power value Pr1 can be generated.

Subsequently, the power transmission apparatus 402 changes thetransmission power value to a second transmission power value Pt2 andtransmits power to the power reception apparatus 401. The powerreception apparatus 401 receives power of a second reception power valuePr2 (this state is referred to as the Connected Load state). Then, thepower transmission apparatus 402 stores the second transmission powervalue Pt2. The second transmission power value Pt2 and the secondreception power value Pr2 are predetermined maximal transmission powerand maximum reception power, respectively. In this operation, the powerreception apparatus 401 controls the loads to receive the maximal power.For example, the power reception apparatus 401 connects the powerreception antenna 205 with the loads to supply the received power to theloads. Subsequently, the power reception apparatus 401 notifies thepower transmission apparatus 402 of the second reception power valuePr2. Upon reception of the second reception power value Pr2 from thepower reception apparatus 401, the power transmission apparatus 402calculates the power loss Pt2−Pr2 (=Ploss2) between the powertransmission apparatus 402 and the power reception apparatus 401,whereby a calibration point 1001 indicating the correspondence betweenthe second transmission power value Pt2 and the second reception powervalue Pr2 can be generated.

Then, the power transmission apparatus 402 generates a straight line1002 for linearly interpolating between the calibration points 1000 and1001. The straight line 1002 indicates a relation between thetransmission power and the reception power in a state where no foreignobject exists in the vicinity of the power transmission apparatus 402and the power reception apparatus 401. The straight line 1002 enablesthe power transmission apparatus 402 to estimate the power valuereceived by the power reception apparatus 401 when the powertransmission apparatus 402 transmits a predetermined transmission powerin a state where no foreign object exists. For example, when the powertransmission apparatus 402 transmits power of a third transmission powervalue Pt3, it can be estimated that the power reception apparatus 401will receive power of a third reception power value Pr3 based on a point1003 corresponding to the third transmission power value Pt3 on thestraight line 1002.

As described above, it is possible to obtain the power loss between thepower transmission apparatus 402 and the power reception apparatus 401according to the loads based on a plurality of combinations of thetransmission power value of the power transmission apparatus 402 and thereception power value of the power reception apparatus 401. In addition,the interpolation based on the plurality of combinations of thetransmission power value and the reception power value enablesestimating the power loss between the power transmission apparatus 402and the power reception apparatus 401 according to all of the loads.Thus, the calibration processing performed by the power transmissionapparatus 402 and the power reception apparatus 401 to enable the powertransmission apparatus 402 to acquire a combination of the transmissionpower value and the reception power value is referred to as “calibrationprocessing (CAL processing) based on Power Loss method”.

The following is an example case where the power transmission apparatus402 transmits power of the third transmission power value Pt3 to thepower reception apparatus 401 after calibration, and the powertransmission apparatus 402 receives a reception power value Pr3′. Thepower transmission apparatus 402 calculates a value Pr3−Pr3′ (=Ploss_FO)by subtracting the reception power value Pr3′ actually received from thepower reception apparatus 401 from the third reception power value Pr3in a state where no foreign object exists. When a foreign object existsin the vicinity of the power transmission apparatus 402 and the powerreception apparatus 401, the value Ploss_FO can be considered as a powerloss of power consumed by the foreign object. This makes it possible todetermine that a foreign object exists, in a case where the powerPloss_FO that may have been consumed by the foreign object is largerthan a predetermined threshold value. Alternatively, the powertransmission apparatus 402 preacquires a power loss Pt3−Pr3 (=Ploss3)between the power transmission apparatus 402 and the power receptionapparatus 401 based on the third reception power value Pr3 in a statewhere no foreign object exists. Then, based on the reception power valuePr3′ received from the power reception apparatus 401 in a state where aforeign object exists, the power transmission apparatus 402 acquires apower loss Pt3−Pr3′ (=Ploss3′) between the power transmission apparatus402 and the power reception apparatus 401. By using Ploss3′-Ploss3(=Ploss_FO), the power transmission apparatus 402 may estimate powerPloss_FO that may have been consumed by the foreign object.

As described above, the power Ploss_FO that may have been consumed bythe foreign object may be acquired as Pr3−Pr3′ (=Ploss_FO) orPloss3′−Ploss3 (=Ploss_FO). While, in the following descriptionsaccording to the present specification, Ploss_FO is basically acquiredas Ploss3′−Ploss3 (=Ploss_FO), the present exemplary embodiment is alsoapplicable to a method for acquiring Ploss_FO as Pr3−Pr3′ (=Ploss_FO).This completes the description of the foreign object detection based onthe Power Loss method.

The foreign object detection based on the Power Loss method is performedduring the power transmission (power transfer phase to be describedbelow) based on data obtained in the calibration phase (describedbelow). The foreign object detection based on the Q value measurementmethod is performed before the power transmission (in a negotiationphase or a renegotiation phase before digital ping transmission to bedescribed below).

The RX and the TX according to the present exemplary embodiment performcommunication for power transmission and reception control conforming tothe WPC standard. The WPC standard prescribes a plurality of phasesincluding the power transfer phase in which the power transmission isperformed and one or more phases before the actual power transmission.Communication for required power transmission and reception control isperformed in each phase. The phases before the power transmission caninclude a selection phase, a ping phase, an identification andconfiguration phase, a negotiation phase, and a calibration phase.Hereinafter, the identification and configuration phase is also referredto as I&C phase. Processing in each phase will be described below.

In the selection phase, the TX intermittently transmits an analog pingand detects that an object is placed on the charging stand 403 of the TX(for example, the RX or a conductor piece is placed on the chargingstand 403). The TX detects at least either one of the voltage and thecurrent values of the power transmission antenna 105 when an analog pingis transmitted. When the voltage value is smaller than a threshold valueor the current value is larger than a threshold value, the TX determinesthat an object exists and enters the ping phase.

In the ping phase, the TX transmits a digital ping having larger powerthan the analog ping. The power of the digital ping is sufficient inmagnitude to activate the control unit of the RX placed on the TX. TheRX notifies the TX of the magnitude of the reception voltage. In thisway, upon reception of a response from the RX that has received thedigital ping of the TX, the TX recognizes that the object detected inthe selection phase is the RX. Upon reception of the notification of thereception voltage value, the TX enters the I&C phase. The TX measuresthe Q value (Q Factor) of the power transmission antenna 105 beforetransmitting a digital ping. The result of this measurement is used whenforeign object detection processing based on the Q value measurementmethod is performed.

In the I&C phase, the TX identifies the RX and acquires deviceconfiguration information (capability information) from the RX. The RXtransmits an ID packet and a configuration packet. The ID packetincludes identifier information on the RX, and configuration packetincludes the device configuration information (capability information)on the RX. Upon reception of the ID packet and the configuration packet,the TX transmits an acknowledge (ACK) as a response. Then, the I&C phaseends.

In the negotiation phase, the GP value is determined based on the GPvalue and the power transmission capability of the TX requested by theRX. the TX performs the foreign object detection processing based on theQ value measurement method in response to a request from the RX. The WPCstandard prescribes a method for performing similar processing to thenegotiation phase again by the request of the RX after once entering thepower transfer phase. A phase entered from the power transfer phase, inwhich these pieces of processing are performed, is referred to as therenegotiation phase.

In the calibration phase, calibration is performed based on the WPCstandard. The RX notifies the TX of a predetermined reception powervalue (the reception power value in a light load state or the receptionpower value in the maximum load state). Then, the TX performs adjustmentfor efficiently performing the power transmission. The reception powervalue notified to the TX can be used for the foreign object detectionprocessing based on the Power Loss method.

The power transfer phase controls the start and continuation of thepower transmission, and the stop of the power transmission if an erroror full charge occurs. In communication, the TX and the RX superimpose asignal on an electromagnetic wave transmitted from the powertransmission antenna 105 or the power reception antenna 205 by using thepower transmission antenna 105 and the power reception antenna 205 thatare used to perform the wireless power transmission conforming to theWPC standard. The communication available range conforming to the WPCstandard between the TX and the RX is almost similar to the powertransmission limit range of the TX.

[Configurations of Power Transmission Apparatus 402 and Power ReceptionApparatus 401]

Configurations of the power transmission apparatus 402 (TX) and thepower reception apparatus 401 (RX) according to the present exemplaryembodiment will be described below. The configurations described beloware to be considered only as illustrative, and a part (or whole in somecases) of the illustrated configurations may be replaced with otherconfigurations performing other similar functions, or omitted.Additional configurations may be added to the illustratedconfigurations. One block to be described below may be divided into aplurality of blocks, and a plurality of block may be integrated into oneblock. Although the function of each of the following function blocks isimplemented as a software program, a part or whole of functions includedin these function block may be implemented by hardware.

FIG. 1 is a function block illustrating an example of a configuration ofthe power transmission apparatus 402 (TX) according to the presentexemplary embodiment. The TX includes a control unit 101, a power sourceunit 102, a power transmission unit 103, a communication unit 104, thepower transmission antenna 105, a memory 106, a resonant capacitor 107,and a switch 108. Referring to FIG. 1 , the control unit 101, the powersource unit 102, the power transmission unit 103, the communication unit104, and the memory 106 are illustrated as separate units. A pluralityof function blocks of these may be implemented in the same chip.

The control unit 101 controls the entire TX, for example, by executing acontrol program stored in the memory 106. The control unit 101 performspower transmission control including communication for deviceauthentication in the TX. The control unit 101 may control the executionof applications other than the wireless power transmission. The controlunit 101 includes, for example, one or more processors such as a centralprocessing unit (CPU) and a microprocessor unit (MPU). The control unit101 may be composed of a hardware component, such as an ApplicationSpecific Integrated Circuit (ASIC). The control unit 101 may include anarray circuit, such as a Field Programmable Gate Array (FPGA), that iscompiled to perform predetermined processing. The control unit 101stores information to be stored during execution of various processing,in the memory 106. The control unit 101 can measure time by using atimer (not illustrated).

The power source unit 102 supplies power to each function block. Thepower source unit 102 is, for example, a commercial power supply orbattery. Power supplied from a commercial power supply is accumulated inthe battery.

The power transmission unit 103 converts alternating current (AC) ordirect current (DC) power input from the power source unit 102 into ACpower in a frequency band that is used for the wireless powertransmission, and inputs the AC power to the power transmission antenna105 to generate an electromagnetic wave to be received by the RX. Forexample, the power transmission unit 103 converts the DC voltagesupplied by the power source unit 102 into an AC voltage via a switchingcircuit having a half- or full-bridge configuration using field effecttransistors (FETs). In this case, the power transmission unit 103includes a gate driver for controlling the ON/OFF state of the FET.

The power transmission unit 103 controls intensity of an electromagneticwave to be output, by adjusting the voltage (power transmissionvoltage), the current (power transmission current), or both to be inputto the power transmission antenna 105. The electromagnetic waveintensity increases with increasing power transmission voltage or powertransmission current, and decreases with decreasing power transmissionvoltage or power transmission current. The power transmission unit 103controls the output of AC power to start or stop the power transmissionfrom the power transmission antenna 105, based on an instruction of thecontrol unit 101. In the present exemplary embodiment, the powertransmission unit 103 is capable of supplying power sufficient to output15 W power to the charging unit 206 of the power reception apparatus 401(RX) conforming to the WPC standard.

The communication unit 104 communicate with the RX to perform theabove-described power transmission control conforming to the WPCstandard. The communication unit 104 modulates an electromagnetic waveoutput from the power transmission antenna 105 and transmits informationto the RX to perform communication. The communication unit 104demodulates an electromagnetic wave received from the power transmissionantenna 105 modulated by the RX to acquire information transmitted bythe RX. More specifically, in the communication performed by thecommunication unit 104, a signal is superimposed on an electromagneticwave received from the power transmission antenna 105. The communicationunit 104 may communicate with the RX in communication conforming to astandard different from the WPC standard by using an antenna differentfrom the power transmission antenna 105, or communicate with the RX byselectively using a plurality of communications.

The memory 106 can store not only control programs but also the statuses(transmission and reception power values) of the TX and the RX. Forexample, the status of the TX may be acquired by the control unit 101,the status of the RX may be acquired by a control unit 201 of the RX andreceived by the TX via the communication unit 104.

The switch 108 is controlled by the control unit 101. The powertransmission antenna 105 is connected to the resonant capacitor 107.When the switch 108 turns ON to make a short-circuit, the powertransmission antenna 105 and the resonant capacitor 107 form a seriesresonant circuit that resonates at a specific frequency f1. At thistiming, a current flows in the closed circuit formed of the powertransmission antenna 105, the resonant capacitor 107, and the switch108. When the switch 108 turns OFF to make an open circuit, the powertransmission antenna 105 and the resonant capacitor 107 are suppliedwith power from the power transmission unit 103.

FIG. 2 is a block diagram illustrating an example of a configuration ofthe power reception apparatus 401 (RX) according to the presentexemplary embodiment. The RX includes the control unit 201, a userinterface (UI) unit 202, a power reception unit 203, a communicationunit 204, the power reception antenna 205, the charging unit 206, abattery 207, a memory 208, a first switch unit 209, a second switch unit210, and a resonant capacitor 211. A plurality of function blocksillustrated in FIG. 2 may be implemented as a hardware module.

The control unit 201 controls the entire RX by, for example, executing acontrol program stored in the memory 208. More specifically, the controlunit 201 controls each function unit illustrated in FIG. 2 . The controlunit 201 may control the execution of applications other than thewireless power transmission. An example of the control unit 201 includesone or more processor, such as a CPU and MPU. The control unit 201 maycontrol the entire RX (when the RX is a smart phone, the entire RXindicates the entire smart phone) in collaboration with an operatingsystem (OS) executed by the control unit 201.

The control unit 201 may be composed of a hardware component such as anASIC. The control unit 201 may include an array circuit, such as a FPGA,that is compiled to perform predetermined processing. The control unit201 stores information that is to be stored during execution of variousprocessing, in the memory 208. The control unit 201 can measure time byusing a timer (not illustrated).

The UI unit 202 performs various output operations to the user. Variousoutput operations include screen display, blinking and color change of alight emitting diode (LED), audio output from a speaker, and vibrationof the RX main body. The UI unit 202 is implemented by a liquid crystalpanel, a speaker, and a vibration motor, for example.

The power reception unit 203 acquires, via the power reception antenna205, AC power (AC voltage and AC current) generated by theelectromagnetic induction based on an electromagnetic wave emitted fromthe power transmission antenna 105 of the TX. Then, the power receptionunit 203 converts AC power into a DC power or an AC power with apredetermined frequency, and outputs power to the charging unit 206 thatperforms processing for charging the battery 207. More specifically, thepower reception unit 203 includes a rectification unit and a voltagecontrol unit that are used for supplying power to the loads of the RX.The above-described GP is the amount of power that is guaranteed foroutput from the power reception unit 203. In the present exemplaryembodiment, the power reception unit 203 is assumed to be capable ofsupplying power necessary for the charging unit 206 to charge thebattery 207, more specifically, capable of supplying 15 W power to thecharging unit 206.

The communication unit 204 performs communication for power receptioncontrol conforming to the WPC standard with the communication unit 104of the TX. The communication unit 204 demodulates an electromagneticwave input from the power reception antenna 205 to acquire informationtransmitted from the TX. Then, by load-modulating the inputelectromagnetic wave, the communication unit 204 superimposes a signalrelated to information to be transmitted to the TX on theelectromagnetic wave, thus communicating with the TX. The communicationunit 204 may communicate with the TX in conformance with a standarddifferent from the WPC standard, using an antenna different from thepower reception antenna 205, or communicate with the TX by selectivelyusing a plurality of communications.

The memory 208 stores not only control programs but also the statuses ofthe TX and the RX. For example, the status of the RX may be acquired bythe control unit 201, and the status of the TX may be acquired by thecontrol unit 101 of the TX and received by the RX via the communicationunit 204.

The first switch unit 209 and the second switch unit 210 are controlledby the control unit 201. The power reception antenna 205 is connected tothe resonant capacitor 211. When the second switch unit 210 turns ON tomake a short-circuit, the power reception antenna 205 and the resonantcapacitor 211 form a series resonant circuit that resonates at aspecific frequency f2. At this timing, a current flows in the closedcircuit formed of the power reception antenna 205, the resonantcapacitor 211, and the second switch unit 210, and no current flows inthe power reception unit 203. When the second switch unit 210 turns OFFto make an open circuit, the power received by the power receptionantenna 205 and the resonant capacitor 211 is supplied to the powerreception unit 203.

The first switch unit 209 controls whether to supply the received powerto the battery 207 as a load. The first switch unit 209 is also providedwith a function of controlling the load value. When the first switchunit 209 connects between the charging unit 206 and the battery 207, thereceived power is supplied to the battery 207. When the first switchunit 209 disconnects the connection between the charging unit 206 andthe battery 207, the received power is not supplied to the battery 207.While, in FIG. 2 , the first switch unit 209 is disposed between thecharging unit 206 and the battery 207, it may be disposed between thepower reception unit 203 and the charging unit 206. Alternatively, thefirst switch unit 209 may be disposed between the closed circuit (formedof the power reception antenna 205, the resonant capacitor 211, and thesecond switch unit 210) and the power reception unit 203. Morespecifically, the first switch unit 209 may be used to control whetherto supply the received power to the power reception unit 203. While, inFIG. 2 , the first switch unit 209 is illustrated as a block, the firstswitch unit 209 can also be implemented as a part of the charging unit206 or a part of the power reception unit 203.

The function of the control unit 101 of the TX will be described belowwith reference to FIG. 3 . FIG. 3 is a block diagram illustrating anexample of a function configuration of the control unit 101 of the powertransmission apparatus 402 (TX). The control unit 101 includes acommunication control unit 301, a power transmission control unit 302, ameasurement unit 303, a setting unit 304, and a foreign object detectionunit 305. The communication control unit 301 controls communication withthe RX conforming to the WPC standard via the communication unit 104.The power transmission control unit 302 controls the power transmissionunit 103 to control the power transmission to the RX. The measurementunit 303 measures a waveform attenuation index (described below). Themeasurement unit 303 also measures power to be transmitted to the RX viathe power transmission unit 103 and measures average transmission powerfor each unit time. The measurement unit 303 also measures the Q valueof the power transmission antenna 105. The setting unit 304 sets athreshold value to be used for the foreign object detection, forexample, by calculation processing based on the waveform attenuationindex measured by the measurement unit 303.

The foreign object detection unit 305 can implement a foreign objectdetection function based on the Power Loss method, a foreign objectdetection function based on the Q value measurement method, and aforeign object detection function based on the waveform attenuationmethod. The foreign object detection unit 305 may be provided with afunction of performing the foreign object detection by using othertechniques. For example, in the TX having the Near Field Communication(NFC) function, the foreign object detection unit 305 may perform theforeign object detection by using an opposed apparatus detectionfunction conforming to the NFC standard. The foreign object detectionunit 305 can also detect that the status of the TX has changed as afunction of a factor other than detecting a foreign object. For example,the TX can also detect an increase or decrease in the number of powerreception apparatuses 401 on the TX. The setting unit 304 sets thresholdvalues to be used by the TX as references for determining presence orabsence of a foreign object when performing the foreign object detectionbased on the Power Loss method, the Q value measurement method, and thewaveform attenuation method. The setting unit 304 may be provided with afunction of setting threshold values as references for determiningpresence or absence of a foreign object. This function is required toperform the foreign object detection processing by using othertechniques. The foreign object detection unit 305 can perform theforeign object detection based on the threshold values set by thesetting unit 304, and the waveform attenuation index, the transmissionpower, and the Q value measured by the measurement unit 303.

Functions of the communication control unit 301, the power transmissioncontrol unit 302, the measurement unit 303, the setting unit 304, andthe foreign object detection unit 305 are implemented as programsoperating in the control unit 101. These processing units are configuredas independent programs and are able to operate in parallel whilemaintaining the synchronization between programs through eventprocessing. However, two or more of these processing units may beincorporated in a program.

[Flow of Processing for Power Transmission Conforming to WPC Standard]

The WPC standard prescribes the selection phase, the ping phase, the I&Cphase, the negotiation phase, the calibration phase, and the powertransfer phase. Operations of the power transmission apparatus 402 andthe power reception apparatus 401 in these phases will be describedbelow with reference to the sequence diagram illustrated in FIG. 5 .FIG. 5 is a sequence diagram illustrating the power transmissionconforming to the WPC standard. An example of a sequence by the powertransmission apparatus 402 (TX) and the power reception apparatus 401(RX) will be described below.

In step F501, the TX repeatedly and intermittently transmits an analogping of the WPC standard to detect an object existing in the powertransmission limit range. The TX performs processing prescribed as theselection and the ping phases by the WPC standard, and waits until theRX is placed on the TX. In step F502, the user of the RX (e.g., a smartphone) brings the RX close to the TX to charge the RX. For example, theuser places the RX on the TX to bring the RX close to the TX. In stepsF503 and F504, the TX detects that an object exists in the powertransmission limit range. In step F505, the TX transmits a digital pingof the WPC standard to the RX. In step F506, the RX receives the digitalping, therefore the RX can recognize that the TX has detected the RX.When the TX receives a predetermined response to the digital ping, theTX determines that the detected object is the RX that is placed on thecharging stand 403. In step F507, when the TX detects that the RX isplaced on the charging stand 403, the TX acquires identificationinformation and capability information from the RX via communication inthe I&C phase prescribed in the WPC standard. In this case, theidentification information for the RX includes a manufacturer code and abasic device ID. The capability information for the RX includes theinformation element for identifying the version of the applicable WPCstandard, Maximum Power Value as the value for identifying the maximumpower that can be supplied to the loads by the RX, and informationindicating whether the RX has the Negotiation function of the WPCstandard. The TX may acquire the identification information and thecapability information for the RX by using a method other than thecommunication in the I&C phase prescribed by the WPC standard. Theidentification information may be any other identification informationfor identifying the main body of the RX, such as a wireless power ID.The capability information may include information other than theabove-described information.

In step F508, the TX determines the GP value in collaboration with theRX via the communication in the negotiation phase prescribed by the WPCstandard. In step F508, communication is not limited to thecommunication in the negotiation phase prescribed by the WPC standard.Other procedures for determining the GP may be performed. Wheninformation indicating that the RX does not support the negotiationphase (e.g., in step F507), the TX does not perform communication in thenegotiation phase. In this case, the GP value may be a small value(prescribed by the WPC standard). According to the present exemplaryembodiment, GP=5 W.

After the determination of the GP, the TX performs calibration based onthe GP. In the calibration processing, in step F509, the RX transmitsinformation including the reception power in the light load state (loaddisconnection state, i.e., a load state where the transmission power isequal to or less than a first threshold value). Hereinafter thisinformation is referred to as first reference reception powerinformation. The first reference reception power information accordingto the present exemplary embodiment is reception power information forthe RX of when the transmission power of the TX is 250 mW. While thefirst reference reception power information is a received Power packet(mode1) prescribed by the WPC standard, other messages may be used. TheTX determines whether to receive the first reference reception powerinformation, based on the power transmission status of the TX itself.When the TX determines to receive the information, the TX transmits anacknowledge (ACK) to the RX. On the other hand, when the TX determinesnot to receive the information, the TX transmits a negative acknowledge(NAK) to the RX.

In step F510, the RX receives an ACK from the TX, and performsprocessing for transmitting information including the reception power inthe load connection state (maximum load state, i.e., a load state wherethe transmission power is equal to or larger than a second thresholdvalue) to the TX. Hereinafter, this information is referred to as secondreference reception power information. According to the presentexemplary embodiment, since the GP is 5 W, the second referencereception power information is the reception power information for theRX when the transmission power of the TX is 5 W. In this case, thesecond reference reception power information is a received power packet(mode2) prescribed by the WPC standard, other messages may also be used.In step F511, the RX transmits an instruction for changing thetransmission power including a positive value to increase thetransmission power from the TX to 5 W.

In steps F512 and F513, the TX receives the instruction for changing thetransmission power. In a case where the transmission power can beincreased, the TX transmits an ACK to the RX as a response to increasethe transmission power. The second reference reception power informationis the reception power information when the transmission power of the TXis 5 W. In step F514, in a case where the TX receives an instruction forthe power increase exceeding 5 W from the RX, then in step F515, the TXtransmits a NAK in response to the instruction for changing thetransmission power to disable the power transmission exceedingpredetermined power.

Upon reception of NAK, then in step F516, the RX determines that thepredetermined transmission power is reached, and transmits informationincluding the reception power in the load connection state to the TX asthe second reference reception power information. The TX is capable ofcalculating the amounts of power loss between the TX and the RX in thelight load and the load connection statuses, based on the transmissionpower value of the TX and the reception power value included in thefirst and the second reference reception power information. In stepF517, the TX interpolates between the amounts of power loss to calculatethe power loss value between the TX and the RX in all transmission power(from 250 mW to 5 W in this case) that can be set by the TX. In stepF518, the TX transmits an ACK in response to the second referencereception power information from the RX to complete the calibrationprocessing. In a case where the TX determines that the charge processingcan be started and then starts the power transmission to the RX, the RXstarts being charged. In step F519, the TX and the RX performs deviceauthentication processing before starting the power transmissionprocessing. In step F520, when the TX and the RX determine that bothapparatuses support the GP having a larger value, the TX and the RX mayset the GP value to a larger value, e.g., 15 W.

In this case, in steps F521 to F524, the RX and the TX exchangeinformation such as the instruction for changing the transmission power,an ACK, and a NAK to increase the transmission power of the TX up to 15W. Then, the TX and the RX perform the calibration processing again forGP=15 W. More specifically, in step F525, the RX transmits informationincluding the reception power in the load connection state of the RXwhen the transmission power of the TX is 15 W. Hereinafter, thisinformation is referred to as third reference reception powerinformation. In step F526, the TX performs calibration based on thereception power included in the first, the second, and the thirdreference reception power information to calculate the amount of powerloss between the TX and the RX in all transmission power (from 250 mW to15 W in this case) that can be set by the TX. In step F527, the TXtransmits an ACK in response to the third reference reception powerinformation from the RX to complete the calibration processing. In stepF528, when the TX determines that the charge processing can be started,the TX starts the power transmission to the RX and then enters the powertransfer phase.

In the power transfer phase, the TX transmits power to the RX. Theforeign object detection is performed based on the Power Loss method. Inthe Power Loss method, firstly, the TX calculates the amount of powerloss between the TX and the RX in a state where no foreign objectexists, based on the difference between the transmission power of the TXand the reception power of the RX through the above-describedcalibration. The calculated value is equivalent to the amount ofreference power loss in the normal state (state where no foreign objectexists) during the power transmission processing. In a case where theamount of power loss between the TX and the RX measured during the powertransmission after the calibration is different from the amount of powerloss in the normal state by at least a threshold value, the TXdetermines that “a foreign object exists” or “a foreign object is likelyto exist”.

This completes the description of the Power Loss method. The Power Lossmethod performs the foreign object detection based on the result ofpower loss measurement during the power transmission from the powertransmission apparatus 402 to the power reception apparatus 401. Theforeign object detection based on the Power Loss method has an advantagethat the foreign object detection can be performed while continuing thepower transmission, which makes it possible to maintain a high powertransmission efficiency. However, this method has a disadvantage thatthe accuracy of the foreign object detection decreases while the powertransmission apparatus 402 is transmitting large power.

In this way, the foreign object detection based on the Power Loss methodcan be performed in the power transfer phase. However, if only theforeign object detection based on the Power Loss method is performed,there are possibilities of a false detection of a foreign object and afalse determination that no foreign object exists although a foreignobject exists. Particularly in the power transfer phase, heat from aforeign object existing in the vicinity of the TX and the RX increaseswhile the TX is transmitting power. In this phase, therefore, it isdemanded to improve the accuracy of the foreign object detection. Thepresent exemplary embodiment, therefore, considers the implementation ofa foreign object detection method, different from the Power Loss method,to improve the accuracy of the foreign object detection.

[Foreign Object Detection Method Based on Waveform Attenuation Method]

In the power transfer phase, the power transmission apparatus 402transmits power to the power reception apparatus 401. Therefore, if theforeign object detection can be performed by using the transmissionpower waveform (voltage or current waveform) related to this powertransmission, the foreign object detection can be performed withoutusing a newly prescribed signal for the foreign object detection. Amethod for detecting a foreign object based on the attenuation state ofthe transmission power waveform (hereinafter this method is referred toas a waveform attenuation method) will be described below with referenceto FIG. 6 . FIG. 6 illustrates the principle of the foreign objectdetection based on the waveform attenuation method. As an example, theforeign object detection using the transmission power waveform relatedto the power transmission from the power transmission apparatus 402 (TX)to the power reception apparatus 401 (RX) will be described below.

Referring to FIG. 6 , the waveform indicates a time-varying voltagevalue 600 (hereinafter simply referred to as a voltage value) of thehigh-frequency voltage applied to the power transmission antenna 105 ofthe TX. The horizontal axis represents time, and the vertical axisrepresents the voltage value. At time T₀, the TX transmitting power tothe RX via the power transmission antenna 105 suspends the powertransmission. More specifically, at time T₀, the power supply for powertransmission from the power source unit 102 is suspended. The frequencyof the transmission power waveform related to the power transmissionfrom the TX is a predetermined frequency, for example, a fixed frequencybetween 85 and 205 kHz used in the WPC standard. A point 601 on theenvelope of the high-frequency voltage indicates the voltage value attime T₁. (T₁, A₁) illustrated in FIG. 6 indicates a voltage value A₁ attime T₁. Likewise, a point 602 on the envelope of the high-frequencyvoltage indicates the voltage value at time T₂. (T₂, A₂) illustrated inFIG. 6 indicates a voltage value A₂ at time T₂. The quality factor (Qvalue) of the power transmission antenna 105 can be obtained based onthe time variation of the voltage value after time T₀. For example, theQ value is calculated by Formula 1 based on time and the voltage valueat the points 601 and 602 on the envelope of the voltage value, and afrequency f of the high-frequency voltage.

Q=πf(T ₂ −T ₁)/In(A ₁ /A ₂)  (Formula 1)

When a foreign object exists in the vicinity of the TX and the RX, thisQ value decreases. This is because, if a foreign object exists, anenergy loss is caused by the foreign object. Therefore, in a case offocusing on the inclination of the voltage value attenuation, thestraight line connecting the points 601 and 602 in a case where aforeign object exists has a steeper inclination resulting in a higherattenuation factor of the waveform amplitude than in a case where noforeign object exists. This is because, when a foreign object exists, anenergy loss by the foreign object occurs. More specifically, thewaveform attenuation method determines presence or absence of a foreignobject based on the attenuation state of the voltage value between thepoints 601 and 602. This method enables actually determining presence orabsence of a foreign object through the comparison of certain numericalvalues representing the attenuation state. For example, thedetermination can be performed by using the Q value. This means that thesmaller Q value provides the higher waveform attenuation (the higherdegree of decrease in the waveform amplitude per unit time).Alternatively, the determination may be performed by using theinclination of the straight line connecting the points 601 and 602obtained by (A₁−A₂)/(T₂−T₁). Alternatively, if the attenuation state ofthe voltage value is observed at fixed time (T₁ and T₂), thedetermination can be performed based on the difference between thevoltage values (A₁−A₂) or the ratio of the voltage values (A₁/A₂).Alternatively, if the voltage value A₁ immediately after the powertransmission is suspended is constant, the determination can beperformed based on the voltage value A₂ after a predetermined time haselapsed. Alternatively, the determination may be performed by using thevalue of the time duration (T₂−T₁) until the voltage value A₁ becomesthe predetermined voltage value A₂.

As described above, presence or absence of a foreign object can bedetermined by the attenuation state of the voltage value during thepower transmission suspension period, and there is a plurality of valuesrepresenting the attenuation state. According to the present exemplaryembodiment, these values representing the attenuation statuses arereferred to as “waveform attenuation indices”. For example, as describedabove, the Q value calculated by Formula 1 represents the attenuationstate of the voltage value related to the power transmission, and isincluded in the “waveform attenuation indices”. The waveform attenuationindices are values corresponding to a waveform attenuation factor. Inthe waveform attenuation method, the waveform attenuation factor itselfmay be measured as a “waveform attenuation index”. The followingdescription will be made centering mainly on a case where the waveformattenuation factor is used as a waveform attenuation index. The presentexemplary embodiment is also similarly applicable to a case where otherwaveform attenuation indices are used.

If the vertical axis illustrated in FIG. 6 represents the current valueflowing in the power transmission antenna 105, the attenuation state ofthe current value during the power transmission suspension periodchanges according to presence or absence of a foreign object, like thecase of the voltage value. Then, in a case where a foreign objectexists, the waveform attenuation factor is higher than that in a casewhere no foreign object exists. Therefore, a foreign object can bedetected even by applying the above-described method to the timevariation of the current value flowing in the power transmission antenna105. More specifically, it is possible to determine presence or absenceof a foreign object to detect a foreign object by using a Q valueobtained based on current waveforms, an inclination of current valueattenuation, a difference in current values, a ratio of current values,an absolute value of current values, and a time duration until apredetermined current value is reached, as waveform attenuation indices.The foreign object detection may be performed based on both a voltagevalue attenuation state and a current value attenuation state, forexample, by determining presence or absence of a foreign object by usingan evaluation value calculated based on a waveform attenuation index ofvoltage values and a waveform attenuation index of current values.Although, in the example above, the waveform attenuation indices aremeasured during a period when the TX suspends the power transmission,the waveform attenuation indices may be measured during a period whenthe TX temporarily reduces power supplied from the power source unit 102from a predetermined power level to a power level lower than thepredetermined power level.

A method for detecting a foreign object based on a transmission powerwaveform during the power transmission through the waveform attenuationmethod will be described below with reference to FIG. 7 . FIG. 7illustrates a transmission power waveform when the foreign objectdetection based on the waveform attenuation method is performed. Thehorizontal axis represents time, and the vertical axis represents thevoltage value of a voltage applied to the power transmission antenna 105or the resonant capacitor 107. Like FIG. 6 , the vertical axis mayrepresent the current value of a current flowing in the powertransmission antenna 105. The transmission power waveform is not stableduring the transient response period immediately after the TX starts thepower transmission. Therefore, during the transient response period whenthe transmission power waveform is not stable, the RX is controlled notto perform communication (communication by load modulation) with the TX.In addition, the TX is controlled not to perform communication(communication by frequency keying) with the RX.

When the timing of the foreign object detection comes, the TX suspendsthe power transmission. Since an amplitude of the transmission powerwaveform is attenuated during the foreign object detection period duringwhich the power transmission is suspended, the TX calculates thewaveform attenuation factor of an attenuated waveform in this period.Then, the TX determines that a foreign object exists in a case where acalculated waveform attenuation factor is larger than a predeterminedthreshold value. In a case where no object is detected after apredetermined foreign object detection period has elapsed, the TXrestarts the power transmission. After restarting the powertransmission, the TX repeats the above-described cycle: waiting for theabove-described transient response period, determining the timing of theforeign object detection, suspending the power transmission, andperforming the foreign object detection processing. This completes thedescription of the basic processing of the foreign object detectionbased on the waveform attenuation method.

If the power reception antenna 205 and the resonant capacitor 211 of thepower reception apparatus 401 are connected with the power receptionunit 203, the charging unit 206, the battery 207, and other elements,the waveform attenuation factor of an attenuated waveform is affected byloads of these elements when measuring the waveform attenuation factorof the transmission power waveform. This means that the waveformattenuation factor changes by the statuses of the power reception unit203, the charging unit 206, and the battery 207. Therefore, in case of alarge waveform attenuation factor, it becomes difficult to determinewhether the large waveform attenuation factor is caused by a foreignobject or by the state transitions of the power reception unit 203, thecharging unit 206, and the battery 207. Therefore, when measuring thewaveform attenuation factor to perform the foreign object detection, thefirst switch unit 209 may be disconnected. This enables eliminating theinfluence of the battery 207. Alternatively, the second switch unit 210may be turned ON to make a short-circuit so that a current flows in theclosed-loop formed of the power reception antenna 205, the resonantcapacitor 211, and the second switch unit 210. This enables eliminatingthe influence of the power reception unit 203, the charging unit 206,and the battery 207. Thus, the high-accuracy foreign object detection isenabled by performing the foreign object detection in a state where thefirst switch unit 209 is disconnected or a state where the second switchunit 210 is turned ON to make a short-circuit (connection). Thehigh-accuracy foreign object detection is also enabled by disconnectingthe first switch unit 209 and short-circuiting (connecting) the secondswitch unit 210.

If the power transmission antenna 105 and the resonant capacitor 107 ofthe power transmission apparatus 402 are connected with the powertransmission unit 103, the communication unit 104, the power source unit102, and other elements, the waveform attenuation factor of theattenuated waveform is affected by loads of these elements whenmeasuring the waveform attenuation factor of the transmission powerwaveform. This means that the waveform attenuation factor changes by thestatuses of the power transmission unit 103, the communication unit 104,and the power source unit 102. Therefore, in case of a large waveformattenuation factor, it becomes difficult to determine whether the largewaveform attenuation factor is caused by a foreign object or by thestate transitions of the power transmission unit 103, the communicationunit 104, and the power source unit 102. Therefore, when measuring thewaveform attenuation factor, the switch 108 may be turned ON to make ashort-circuit so that a current flows in the closed-loop formed of thepower transmission antenna 105, the resonant capacitor 107, and theswitch 108. This enables eliminating the influence of the powertransmission unit 103, the communication unit 104, and the power sourceunit 102. Alternatively, a switch may be provided between theclosed-loop circuit (formed of the power transmission antenna 105, theresonant capacitor 107, and the switch 108) and the power transmissionunit 103. When performing the foreign object detection, this switchenables eliminating the influence of the power transmission unit 103,the communication unit 104, and the power source unit 102 bydisconnecting the closed-loop circuit and the power transmission unit103. Thus, the high-accuracy foreign object detection is enabled byturning ON the switch 108 to make a short-circuit (connection) or byperforming the foreign object detection in a state where the closed-loopcircuit and the power transmission unit 103 are disconnected by aswitch. The high-accuracy foreign object detection is also enabled byturning ON the switch 108 to make a short-circuit (connection) and bydisconnecting the closed-loop circuit and the power transmission unit103 by using a switch.

[Method for Setting Threshold Value for Foreign Object Detection Basedon Waveform Attenuation Method]

FIG. 11 is a diagram for explaining a method for setting a thresholdvalue for the foreign object detection based on the waveform attenuationmethod. Firstly, when power is transmitted from the TX, the RX controlsthe loads of the RX to enter the light load state so that no power orvery small power is supplied to the loads of the RX. At this timing, theTX transmits transmission power Pt1. Then, in this state, the TXsuspends the power transmission and measures the waveform attenuationfactor. The measured waveform attenuation factor is obtained as awaveform attenuation factor 61. At this timing, the TX recognizes thetransmission power Pt1 transmitted by the TX, and stores a calibrationpoint 1100 that associates the transmission power Pt1 with the waveformattenuation factor 61, in the memory 208. Then, when power istransmitted from the TX, the RX controls the loads of the RX to causethe loads to enter the load connection state so that the maximum poweror power equal to or larger than a predetermined threshold value issupplied to the loads of the RX. The transmission power from the TX atthis timing is transmission power Pt2. Then, in this state, the TXsuspends the power transmission and measures the waveform attenuationfactor. At this timing, the TX stores a calibration point 1101 thatassociates the transmission power Pt2 with a waveform attenuation factor62, in the memory 208. Subsequently, the TX linearly interpolatesbetween the calibration points 1100 and 1101 to generate a straight line1102. The straight line 1102 indicates the relation between thetransmission power and the waveform attenuation factor of thetransmission power waveform in a state where no foreign object exists atthe periphery of the TX and the RX. The straight line 1102 enables theTX to estimate the waveform attenuation factor of the transmission powerwaveform for each transmission power value in a state where no foreignobject exists. For example, with the transmission power value Pt3, theTX can estimate a waveform attenuation factor 63 based on a point 1103on the straight line 1102 corresponding to the transmission power valuePt3. Then, based on the result of the estimation, the TX can calculatethe threshold value to be used to determine presence or absence of aforeign object for each transmission power value. For example, awaveform attenuation factor larger than the result of estimating thewaveform attenuation factor when no foreign object exists with a certaintransmission power value by a predetermined value (the valuecorresponding to the measurement error) may be set as a threshold valuefor determining presence or absence of a foreign object. Hereinafter,calibration processing performed by the power transmission apparatus 402and the power reception apparatus 401 to enable the power transmissionapparatus 402 to acquire a combination of the transmission power valueand the waveform attenuation factor is referred to as “calibrationprocessing (CAL processing) based on the waveform attenuation method”.

the RX may perform control for supplying no power to the loads orsetting the light load state, and control for setting the loadconnection state, after notifying the TX that each of such control is tobe performed. Either one of these two pieces of control may be performedfirst.

An operation for calculating a threshold value to be used to determinepresence or absence of a foreign object for each load (each transmissionpower value) according to the present exemplary embodiment may also beperformed in the calibration phase. As described above, in thecalibration phase, the TX acquires data which is to be required whenperforming the foreign object detection based on the Power Loss method.In this case, the TX acquires data related to the power loss when theload state of the RX is the light load state and when the load state ofthe RX is the load connection state. Accordingly, the measurement of thecalibration points 1100 and 1101 illustrated in FIG. 11 may be performedtogether with the measurement of the power loss when the RX enters thelight load state and when the RX enters the load connection state in thecalibration phase. More specifically, upon reception of the firstreference reception power information from the RX, the TX measures thecalibration point 1100 in addition to predetermined processing which isperformed in the calibration phase. Also, upon reception of the secondreference reception power information from the RX, the TX measures thecalibration point 1101 in addition to predetermined processing which isperformed in the calibration phase. This eliminates the need ofseparately providing a period for measuring the calibration points 1100and 1101, making it possible to measure the calibration points 1100 and1101 in a shorter time.

[Processing of Power Transmission Apparatus When Waveform AttenuationMethod is Applied to WPC Standard]

Processing of the power transmission apparatus 402 for performing theforeign object detection by applying the waveform attenuation method tothe WPC standard will be described below. In a case where the foreignobject detection based on the waveform attenuation method is performed,the power transmission apparatus 402 pre-measures the waveformattenuation factor in a state where no foreign object exists and thencalculates a threshold value based on the waveform attenuation factor.Subsequently, the power transmission apparatus 402 performs the foreignobject detection based on the waveform attenuation method. In a casewhere the measured waveform attenuation factor is larger than thethreshold value, the power transmission apparatus 402 determines that “aforeign object exists” or “a foreign object is likely to exist”.Meanwhile, in a case where the measured waveform attenuation factor issmaller than the threshold value, the power transmission apparatus 402determines that “no foreign object exists” or “no foreign object ishighly likely to exist”.

The timing of pre-measuring the waveform attenuation factor in a statewhere no foreign object exists will be described below. In the WPCstandard, as described above, the power transmission apparatus 402performs the foreign object detection based on the Q value measurementmethod in the negotiation phase. In a case where the power transmissionapparatus 402 determines that no foreign object exists as a result ofthe foreign object detection, the power transmission apparatus 402proceeds to the calibration phase and then the power transfer phase.More specifically, the power transmission apparatus 402 having proceededto the negotiation phase or subsequent phases means that the powertransmission apparatus 402 determines that no foreign object exists as aresult of the foreign object detection based on the Q value measurementmethod. Therefore, if the waveform attenuation factor is measured in anyone of the negotiation, the calibration, and the power transfer phases,it is highly likely that the waveform attenuation factor can be measuredin a state where no foreign object exists. Therefore, the timing ofmeasuring the waveform attenuation factor in a state where no foreignobject exists may be any one of the negotiation, the calibration, andthe power transfer phases.

According to the present exemplary embodiment, the timing of measuringthe waveform attenuation factor in a state where no foreign objectexists is set to the first stage in the power transfer phase. This isbecause the probability that a foreign object is placed in the vicinityof the power transmission apparatus 402 and the power receptionapparatus 401 increases with increasing elapsed time since the powertransmission apparatus 402 determines that “no object exists” based onthe Q value measurement method. Then, the power transmission apparatus402 measures the waveform attenuation factor of a transmission powerwaveform at the timing when the foreign object detection is performed,specified by the power reception apparatus 401 or the power transmissionapparatus 402. Subsequently, the power transmission apparatus 402compares the measured waveform attenuation factor with a threshold valuecalculated based on the waveform attenuation factor in a state where noforeign object exists, to determine presence or absence of a foreignobject.

In the waveform attenuation method, the power transmission apparatus 402suspends the power transmission, measures the waveform attenuationfactor of a transmission power waveform, and performs the foreign objectdetection. For this reason, this method has a disadvantage thatsuspending the power transmission leads to a decrease in the powertransmission efficiency. On the other hand, the method has an advantagethat the high-accuracy foreign object detection is possible even whenthe foreign object detection processing is performed during large powertransmission. More specifically, the use of the waveform attenuationmethod enables detecting a foreign object even in a situation where thePower Loss method finds it difficult to correctly detect a foreignobject.

According to the above-described exemplary embodiment, in a case wherethe foreign object detection based on the waveform attenuation method isperformed, the waveform attenuation factor is measured before startingthe power transmission in a state where there is no foreign object andthen a threshold value is calculated based on the waveform attenuationfactor. In a case where the measured waveform attenuation factormeasured in the foreign object detection by the wave form attenuationmethod is larger than a threshold value, the power transmissionapparatus 402 determines that “a foreign object exists” or “a foreignobject is likely to exist”. Meanwhile, in a case where the measuredwaveform attenuation factor is smaller than the threshold value, thepower transmission apparatus 402 determines that “no foreign objectexists” or “no foreign object is highly likely to exist”. However, theforeign object detection may be performed by using the threshold valueobtained based on the waveform attenuation factor measured at the timingwhen no foreign object exists after starting the power transmission. Forexample, the TX checks that no foreign object exists based on the PowerLoss method during the power transmission. Then, the TX performs thefirst waveform attenuation factor measurement and then calculates thethreshold value based on the measured waveform attenuation factor. Sincethe first waveform attenuation factor measurement is performed based onthe Power Loss method immediately after checking that no foreign objectexists in advance, the measured waveform attenuation factor is estimatedto be the waveform attenuation factor in a state where no foreign objectexists. Then, the TX restarts the power transmission and performs thesecond waveform attenuation factor measurement at the timing when the TXdetermines that the foreign object detection is required. Then, the TXcompares the result of the second waveform attenuation factormeasurement with the result of the first waveform attenuation factormeasurement or the threshold value calculated based on the result of thefirst waveform attenuation factor measurement, thus determining presenceor absence of a foreign object. More specifically, in a case where theforeign object detection based on the waveform attenuation method isperformed, the TX may compare the waveform attenuation factor measuredat that timing of the foreign object detection with the waveformattenuation factor measured in a prior state where no foreign objectexists or a threshold value.

In the exemplary embodiment, the frequency of the transmission powerwaveform related to the power transmission from the power transmissionapparatus 402 is a fixed frequency. However, the TX may determinepresence or absence of a foreign object by performing processing for theforeign object detection according to the present exemplary embodimentfor each of a plurality of frequencies, and then combining the results.The foreign object detection can be performed with higher accuracy byperforming the foreign object detection using not only the waveformattenuation factor at a frequency but also the waveform attenuationfactor at a plurality of frequencies.

According to the present exemplary embodiment, a wait time is providedbefore proceeding to each operation since the transmission powerwaveform is unstable in transient response immediately after the powertransmission apparatus 402 suspends or starts the power transmission.The unstable transmission power waveform is caused by suddenly startingor suspending the power transmission. To avoid the unstable powertransmission, the power transmission apparatus 402 may control thetransmission power to gradually increase the transmission power whenstarting the power transmission. Alternatively, the power transmissionapparatus 402 may control the transmission power to gradually decreasewhen suspending the power transmission.

[Foreign Object Detection Processing in Response to Communication Error]

As described above, the power transmission apparatus 402 and the powerreception apparatus 401 perform communication for power transmission andreception control conforming to the WPC standard. This communication iswirelessly performed via the power transmission antenna 105 of the powertransmission apparatus 402 and the power reception antenna 205 of thepower reception apparatus 401. Therefore, in a case where a foreignobject exists in the vicinity of the power transmission apparatus 402and the power reception apparatus 401 (e.g., between the powertransmission apparatus 402 and the power reception apparatus 401), theforeign object interferes with wireless communication between the powertransmission apparatus 402 and the power reception apparatus 401,possibly resulting in a communication error. Therefore, according to thepresent exemplary embodiment, in a case where a communication erroroccurs, a foreign object is likely to exist in the vicinity of the powertransmission apparatus 402 and the power reception apparatus 401. Inthis case, the power transmission apparatus 402 and the power receptionapparatus 401 control the execution of the foreign object detection.

As described above, the Power Loss method and the waveform attenuationmethod are used as a foreign object detection method which is performedduring the power transmission from the power transmission apparatus 402to the power reception apparatus 401. As described above with referenceto FIG. 10 , in the Power Loss method, the power reception apparatus 401notifies the power transmission apparatus 402 of the reception powervalue Pr3′ measured by the power reception apparatus 401. The powertransmission apparatus 402 calculates Pr3-Pr3′ (=Ploss_FO) bysubtracting the reception power value Pr3′ actually received from thepower reception apparatus 401 from the reception power value Pr3 in astate where no foreign object exists. In a case where a foreign objectexists in the vicinity of the power transmission apparatus 402 and thepower reception apparatus 401, Ploss_FO can be assumed as the power lossdue to the power consumed by the foreign object. Therefore, the powertransmission apparatus 402 can determine that a foreign object existswhen the power Ploss_FO that may have been consumed by the foreignobject is larger than a predetermined threshold value. Morespecifically, when foreign object detection based on the Power Lossmethod is performed, the power reception apparatus 401 communicates withthe power transmission apparatus 402 to notify the power transmissionapparatus 402 of the reception power value Pr3′, as described above.Since a communication error has already occurred between the powertransmission apparatus 402 and the power reception apparatus 401, anerror may also occur by a similar cause in this communication for theforeign object detection.

Meanwhile, in the waveform attenuation method, the power transmissionapparatus 402 suspends the power transmission and compares the waveformattenuation factor at that timing with the pre-measured waveformattenuation factor in a state where no foreign object exists todetermines presence or absence of a foreign object. Therefore, theforeign object detection can be performed without communication betweenthe power transmission apparatus 402 and the power reception apparatus401. Accordingly, in a case where a communication error occurs, thepower transmission apparatus 402 performs the foreign object detectionbased on the waveform attenuation method that does not requirecommunication. This enables increasing the possibility that the foreignobject detection will be successful.

Even in a case where a foreign object exists in the vicinity of thepower transmission apparatus 402 and the power reception apparatus 401during the power transmission, a communication error may not occur.However, even in a case where a communication error does not occur, thepresence of a foreign object may cause a failure, such as a larger powerloss and heat generation from the foreign object. Therefore, the powertransmission apparatus 402 periodically performs the foreign objectdetection processing in the power transfer phase during which thewireless power transmission is performed, thus checking whether aforeign object exists in the vicinity of the power transmissionapparatus 402 and the power reception apparatus 401. The use of thewaveform attenuation method for the periodical foreign object detectiontemporarily suspends the power transmission from the power transmissionapparatus 402 each time the foreign object detection is performed,resulting in a decrease in the power transmission efficiency. Meanwhile,the use of the Power Loss method enables detecting a foreign objectwhile continuing the power transmission from the power transmissionapparatus 402 to the power reception apparatus 401. Therefore, in a casewhere a communication error does not occur, the power transmissionapparatus 402 and the power reception apparatus 401 periodically performthe foreign object detection based on the Power Loss method in the powertransfer phase. This enables early detection of a foreign object whilemaintaining the high power transmission efficiency.

Operations of the power transmission apparatus 402 and the powerreception apparatus 401 using the above-described plurality of foreignobject detection methods will be described below. FIG. 8 illustrates anexample of an operation of the power transmission apparatus 402 in thepower transfer phase. The processing illustrated in FIG. 8 is startedwhen the power transmission apparatus 402 detects the power receptionapparatus 401 placed on the charging stand 403, the power transmissionapparatus 402 performs communication, and the processing in each phaseprescribed in the WPC standard is completed. Phases performed beforestarting the processing illustrated in FIG. 8 includes the selection,the ping, the I&C, the negotiation, and the calibration phases. However,the processing illustrated in FIG. 8 may be started without performingat least a part of the above-described phases.

In step S801, the power transmission apparatus 402 starts the powertransmission in the power transfer phase. In step S802, the powertransmission apparatus 402 determines whether a command for performingthe foreign object detection based on the Power Loss method is receivedfrom the power reception apparatus 401. This command includes thereception power value measured by the power reception apparatus 401. Ina case where the power transmission apparatus 402 receives this command(YES step S802), the processing proceeds to step S803. In step S803, thepower transmission apparatus 402 performs the foreign object detectionbased on the Power Loss method, based on the reception power valuereceived from the power reception apparatus 401 and the transmissionpower value measured by the power transmission apparatus 402.

In step S804, the power transmission apparatus 402 determines whether aforeign object exists in the vicinity of the power transmissionapparatus 402 based on the result of the foreign object detectionprocessing. In a case where the power transmission apparatus 402determines that a foreign object exists (YES in step S804), theprocessing proceeds to step S805. In step S805, the power transmissionapparatus 402 transmits a negative acknowledge (NAK) as informationindicating the presence of a foreign object to the power receptionapparatus 401. In step S806, the power transmission apparatus 402performs control to suspend the power transmission or reduce thetransmission power. Meanwhile, in a case where the power transmissionapparatus 402 determines that no foreign object exists (NO in stepS804), the processing proceeds to step S807. In step S807, the powertransmission apparatus 402 transmits an acknowledge (ACK) as informationindicating absence of a foreign object to the power reception apparatus401 and continues the power transmission. Then, the processing returnsto step S802.

Meanwhile, in a case where the command for performing the foreign objectdetection based on the Power Loss method is not received (NO in stepS802), the processing proceeds to step S808. In step S808, the powertransmission apparatus 402 determines whether a communication erroroccurred in the communication between the power transmission apparatus402 and the power reception apparatus 401. In a case where the powertransmission apparatus 402 does not receive a command transmitted fromthe power reception apparatus 401, the power transmission apparatus 402determines that a communication error occurred (or detects acommunication error). For example, to periodically perform the foreignobject detection based on the Power Loss method, the power receptionapparatus 401 periodically transmits the command for performing theforeign object detection based on the Power Loss method to the powertransmission apparatus 402. In a case where the power transmissionapparatus 402 does not receive the command which is periodicallyreceived or in a case where the power transmission apparatus 402receives a command including an invalid packet, the power transmissionapparatus 402 determines that a communication error occurred. However,the method for detecting a communication error by the power transmissionapparatus 402 is not limited thereto.

In a case where the power transmission apparatus 402 detects acommunication error (YES in step S808), i.e., when a foreign object maypossibly exist, the processing proceeds to step S809. In step S809, thepower transmission apparatus 402 performs the foreign object detectionbased on the waveform attenuation method. Then, the power transmissionapparatus 402 performs the processing from step S804 to step S807 basedon the result of the foreign object detection like the case where theforeign object detection based on the Power Loss method is performed.

Meanwhile, in a case where the power transmission apparatus 402 does notdetect a communication error (NO in step S808), the processing proceedsto step S810. In step S810, the power transmission apparatus 402determines whether a command for performing the foreign object detectionbased on the waveform attenuation method is received from the powerreception apparatus 401. The power reception apparatus 401 transmitsthis command, for example, when the power reception apparatus 401detects a communication error (described below). In a case where thepower transmission apparatus 402 determines that this command isreceived (YES in step S810), the processing proceeds to step S809. Instep S809, the power transmission apparatus 402 performs the foreignobject detection based on the waveform attenuation method. Then, thepower transmission apparatus 402 performs the processing from step S804to step S807 based on result of the foreign object detection.

FIG. 9 illustrates an example of an operation in the power transferphase of the power reception apparatus 401. The processing illustratedin FIG. 9 is started at a similar timing to the processing illustratedin FIG. 8 . In step S901, the power reception apparatus 401 starts thepower reception in the power transfer phase. In step S902, the powerreception apparatus 401 transmits the command for performing the foreignobject detection based on the Power Loss method, as a command to beperiodically transmitted to the power transmission apparatus 402. Thiscommand is issued by the power reception apparatus 401 and requests thepower transmission apparatus 402 to perform the foreign object detectionprocessing based on the Power Loss method.

In step S903, the power reception apparatus 401 determines whether acommunication error occurred in the communication between the powertransmission apparatus 402 and the power reception apparatus 401. Thepower reception apparatus 401 determines a communication error asfollows. The power reception apparatus 401 transmits various commands tothe power transmission apparatus 402 according to the WPC standard. Uponreception of a command from the power reception apparatus 401, the powertransmission apparatus 402 transmits a response (acknowledge or negativeacknowledge) to the power reception apparatus 401. For example, whenperiodically performing the foreign object detection based on the PowerLoss method, the power reception apparatus 401 periodically transmitsthe command for performing the foreign object detection based on thePower Loss method to the power transmission apparatus 402. Uponreception of the command, the power transmission apparatus 402 transmitsa response to the power reception apparatus 401. Accordingly, in a casewhere the power reception apparatus 401 does not receive a response fromthe power transmission apparatus 402 after transmitting the command forperforming the foreign object detection based on the Power Loss methodto the power transmission apparatus 402, the power reception apparatus401 determines that a communication error occurred (i.e., the powertransmission apparatus 402 detects a communication error). In a casewhere the power reception apparatus 401 receives a response including aninvalid packet from the power transmission apparatus 402, the powerreception apparatus 401 determines that a communication error occurred.However, the method for detecting a communication error by the powerreception apparatus 401 is not limited thereto.

In a case where the power reception apparatus 401 detects acommunication error (YES in step S903), there is a possibility that aforeign object is likely to exist and that the foreign object detectionbased on the Power Loss method may not normally be performed. Then, theprocessing proceeds to step S904. In step S904, the power receptionapparatus 401 transmits the command for performing the foreign objectdetection based on the waveform attenuation method to the powertransmission apparatus 402. This command is issued by the powerreception apparatus 401 and requests the power transmission apparatus402 to perform the foreign object detection processing based on thewaveform attenuation method. Then, the power reception apparatus 401waits for a response according to the result of performing the foreignobject detection based on the waveform attenuation method from the powertransmission apparatus 402. In a case where the power receptionapparatus 401 does not detect a communication error (NO in step S903),the power reception apparatus 401 waits for a response according to theresult of performing the foreign object detection based on the PowerLoss method from the power transmission apparatus 402. Then, theprocessing proceeds to step S905.

In step S905, the power reception apparatus 401 determines whether anegative acknowledge as information indicating the presence of a foreignobject is received from the power transmission apparatus 402. In a casewhere the power reception apparatus 401 receives a negative acknowledge(YES in step S905), the processing proceeds to step S906. In step S906,the power reception apparatus 401 transmits an End Power Transfer (EPT)command as a command for ending the power transmission, to the powertransmission apparatus 402. Then, the power reception apparatus 401enters a non-power reception state. Meanwhile, in a case where the powerreception apparatus 401 does not receive a negative acknowledge, forexample, when the power reception apparatus 401 receives an acknowledge(NO in step S905), the power reception apparatus 401 continues the powerreception. Then, the processing returns to step S902.

This completes the description of examples of operations of the powertransmission apparatus 402 and the power reception apparatus 401. Asdescribed above, in a case where a communication error is detected inthe communication between the power transmission apparatus 402 and thepower reception apparatus 401, the power transmission apparatus 402 andthe power reception apparatus 401 perform the foreign object detectionbased on the waveform attenuation method. This makes it possible todetect a foreign object in the vicinity of the power transmissionapparatus 402 and the power reception apparatus 401 in an early stageand suspend the power transmission (or reduce the transmission power),thus improving the probability of preventing an extreme temperature riseof the foreign object. Although, in the above descriptions, both thepower transmission apparatus 402 and the power reception apparatus 401perform the error detection, either one of the power transmissionapparatus 402 and the power reception apparatus 401 may perform theerror detection.

As described above, the power transmission apparatus 402 mayshort-circuit the switch 108 at the timing when the foreign objectdetection based on the waveform attenuation method is performed, anddisconnect the switch between the closed-loop circuit including thepower transmission antenna 105 and the power transmission unit 103. Thiseliminates the influences of the power transmission unit 103, thecommunication unit 104, and the power source unit 102 on the attenuatedwaveform, enabling the foreign object detection with higher accuracy.Likewise, the power reception apparatus 401 may short-circuit the secondswitch unit 210 and disconnect the first switch unit 209 at the timingwhen the foreign object detection based on the waveform attenuationmethod is performed. This eliminates the influences of the powerreception unit 203, the charging unit 206, and the battery 207 on theattenuated waveform, enabling the foreign object detection with higheraccuracy. In this case, the power transmission apparatus 402 and thepower reception apparatus 401 perform communication to identify thetiming of when the foreign object detection is performed.

According to the above-described exemplary embodiment, when the foreignobject detection based on the waveform attenuation method is performed,the power transmission apparatus 402 measures the attenuation factor ofa voltage applied to the power transmission antenna 105 or a currentflowing in the power transmission antenna 105 as the attenuation stateof the transmission power waveform related to the wireless powertransmission. However, since the power transmission antenna 105 and thepower reception antenna 205 facing each other are electromagneticallyconnected, the electromagnetic energy of the power transmission antenna105 is also excited in the power reception antenna 205. Therefore, theforeign object detection based on the waveform attenuation method canalso be implemented by the power reception apparatus 401 measuring theattenuation factor of a voltage applied to the power reception antenna205 or a current flowing in the power reception antenna 205 as theattenuation state of the power reception waveform related to thewireless transmission.

When the power transmission apparatus 402 measures the waveformattenuation factor, the power transmission apparatus 402 may notify thepower reception apparatus 401 of the result of the waveform attenuationfactor measurement or a threshold value obtained based on themeasurement result. This enables the power reception apparatus 401 todetermine presence or absence of a foreign object based on themeasurement result received from the power transmission apparatus 402.Likewise, when the power reception apparatus 401 measures the waveformattenuation factor, the power reception apparatus 401 may notify thepower transmission apparatus 402 of the result of the waveformattenuation factor measurement or a threshold value obtained based onthe measurement result. This enables the power transmission apparatus402 to determine presence or absence of a foreign object based on themeasurement result received from the power reception apparatus 401.

In the above descriptions with reference to FIGS. 8 and 9 , the waveformattenuation method is employed to perform the high-accuracy foreignobject detection in a case where a communication error is detected.Thus, even if the power transmission apparatus 402 and the powerreception apparatus 401 fails to detect a foreign object in theperiodical foreign object detection processing based on the Power Lossmethod, performing the foreign object detection processing based on thewaveform attenuation method in response to a communication error enablesdetecting a foreign object and suspending the power transmission (orreducing the transmission power). However, to avoid the decrease in thepower transmission efficiency, the power transmission apparatus 402 andthe power reception apparatus 401 may perform the foreign objectdetection based on the Power Loss method in response to thecommunication error detection. In this case, the power transmissionapparatus 402 detected a communication error in step S808 illustrated inFIG. 8 may perform the foreign object detection based on the Power Lossmethod instead of performing the foreign object detection based on thewaveform attenuation method in step S809. The power reception apparatus401 detected a communication error in step S903 illustrated in FIG. 9may transmit the command for performing the foreign object detectionbased on the Power Loss method instead of transmitting the command forperforming the foreign object detection based on the waveformattenuation method in step S904. When the foreign object detection basedon the Power Loss method is performed in step S809, the powertransmission apparatus 402 requests the power reception apparatus 401 totransmit a command including the reception power value, and detects aforeign object based on the reception power value received in responseto the request and the transmission power value measured by the powertransmission apparatus 402. In a case where the power receptionapparatus 401 transmits the command for performing the foreign objectdetection based on the Power Loss method in step S903, the powertransmission apparatus 402 that received the command performs theforeign object detection based on the Power Loss method. Even if thepower transmission apparatus 402 and the power reception apparatus 401fail to detect a foreign object in the periodical foreign objectdetection processing based on the Power Loss method, performing theforeign object detection processing again in response to a communicationerror increases the probability of detecting a foreign object.

When performing the foreign object detection based on the Power Lossmethod in response to the communication error detection, thecommunication for foreign object detection is performed between thepower transmission apparatus 402 and the power reception apparatus 401.However, a communication error may occur again in this communication,and a possible result is that the power transmission apparatus 402 orthe power reception apparatus 401 may be unable to receive data from thecommunication partner or may receive data including an invalid packet.In a case where the command for performing the foreign object detectiontransmitted from the power reception apparatus 401 to the powertransmission apparatus 402 is lost because of a communication error, thepower transmission apparatus 402 is unable to recognize that the foreignobject detection is requested and therefore does not perform the foreignobject detection. Consequently, the power transmission apparatus 402does not transmit a response to the command for performing the foreignobject detection to the power reception apparatus 401.

Therefore, in a case where it is determined that such a communicationerror occurred again, the power reception apparatus 401 may transmit theEPT command as a command for ending the power transmission to the powertransmission apparatus 402 and enter the non-power reception state. Uponreception of the EPT command, the power transmission apparatus 402suspends the power transmission. Even if the power transmissionapparatus 402 is unable to receive the EPT command, the powertransmission apparatus 402 may detect that the power reception apparatus401 entered the non-power reception state, suspend the powertransmission, and enter the selection phase. In a case where acommunication error occurs again in the communication for performing theforeign object detection in response to the communication errordetection, the frequency of the communication error occurrence is high.In this case, it can be considered that a foreign object is highlylikely to exist or a certain factor other than a foreign objectinterferes with communication. Therefore, in this case, the occurrenceof a failure due to the power transmission can be prevented bysuspending the power transmission or reducing the transmission power, asdescribed above.

In a case where the above-described foreign object detection based onthe Power Loss method or foreign object detection based on the waveformattenuation method is performed, the foreign object detection maypossibly fail. For example, in a case where the power receptionapparatus 401 placed on the power transmission apparatus 402 movesduring the foreign object detection processing, the measured value to beused for the foreign object detection becomes an abnormal value,possibly resulting in a failure of the foreign object detection. Also,in this case, the power transmission apparatus 402 and the powerreception apparatus 401 may suspend the power transmission or reduce thetransmission power since these apparatuses may be unsuitable forperforming the wireless power transmission. This enables preventing theoccurrence of a failure in the power transmission.

[Foreign Object Detection Processing in Response to Power Reduction]

Processing for the foreign object detection performed by the powertransmission apparatus 402 and the power reception apparatus 401 inresponse to the communication error detection has been described abovewith reference to FIGS. 8 and 9 . Processing for the foreign objectdetection performed in response to the reception power reduction in thepower reception apparatus 401 will be described below.

In a case where a foreign object exists in the vicinity of the powertransmission apparatus 402 and the power reception apparatus 401, theforeign object interferes with the wireless power transmission betweenthe power transmission apparatus 402 and the power reception apparatus401, possibly resulting in a reception power reduction in the powerreception apparatus 401. Therefore, in a case where a reception powerreduction in the power reception apparatus 401 occurs, a foreign objectis likely to exist in the vicinity of the power transmission apparatus402 and the power reception apparatus 401. Thus, the power transmissionapparatus 402 and the power reception apparatus 401 control theexecution of the foreign object detection.

Operations of the power reception apparatus 401 and the power receptionapparatus 401 in case of performing the foreign object detection in acase where the power transmission apparatus 402 detects the receptionpower reduction in the power reception apparatus 401 will be describedbelow. The power transmission apparatus 402 periodically receives thereception power value Pr3′ from the power reception apparatus 401 toperform the foreign object detection based on the Power Loss method inthe power transfer phase. Then, the power transmission apparatus 402determines whether a reception power reduction in the power receptionapparatus 401 occurs, based on the reception power value Pr3′ receivedfrom the power reception apparatus 401 or Ploss_FO as the differencebetween pre-identified Pr3 and Pr3′. In a case where the reception powervalue Pr3′ received from the power reception apparatus 401 is smallerthan a threshold value or in a case where Ploss_FO is larger than athreshold value, the power transmission apparatus 402 determines that areception power reduction in the power reception apparatus 401 occurs,and performs the foreign object detection based on the waveformattenuation method.

More specifically, the power transmission apparatus 402 periodicallyperforms the foreign object detection based on the Power Loss method formaintaining the high power transmission efficiency and, according to thereception power received from the power reception apparatus 401 for theforeign object detection, performs the foreign object detection based onthe waveform attenuation method with higher accuracy of the foreignobject detection. For example, for the value of Pr3′ or Ploss_FO, thepower transmission apparatus 402 may provide a first threshold value fordetermining that a foreign object is likely to exist and a secondthreshold value for determining that a foreign object exists. Then, in acase where the value of Pr3′ or Ploss_FO is larger than the secondthreshold value, the power transmission apparatus 402 determines that aforeign object is detected based on the Power Loss method, and thensuspends the power transmission or reduces the transmission power. In acase where the value of Pr3′ or Ploss_FO is larger than the firstthreshold value and is not larger than the second threshold value, thepower transmission apparatus 402 performs the foreign object detectionbased on the waveform attenuation method. Thus, even in a case where aforeign object cannot be detected in the foreign object detection basedon the Power Loss method, performing the higher-accuracy waveformattenuation method in response to the reception power reduction enablesdetecting a foreign object. Each of the above-described threshold valuesmay be set based on data (the straight line 1002 illustrated in FIG. 10) obtained in the Calibration processing of the Power Loss method.

Although, in the above descriptions, the power transmission apparatus402 performs the foreign object detection in response to the receptionpower reduction in the power reception apparatus 401, the powertransmission apparatus 402 may perform the foreign object detection inresponse to the variation in the transmission power of the powertransmission apparatus 402. The power transmission apparatus 402 canmeasure the transmission power value currently being transmitted by thepower transmission apparatus 402. Accordingly, in a case where thedifference between the transmission power value and a predeterminedreference value is larger than a threshold value, the power transmissionapparatus 402 determines that a foreign object may possibly exist andmay perform the foreign object detection based on the waveformattenuation method. This configuration also enables obtaining a similarresult to that which is obtained in case of performing the foreignobject detection in response to the reception power reduction.

Operations of the power transmission apparatus 402 and the powerreception apparatus 401 in case of performing the foreign objectdetection when the power reception apparatus 401 detects the receptionpower reduction in the power reception apparatus 401 will be describedbelow. The power reception apparatus 401 periodically measures the powerreceived from the power transmission apparatus 402 in the power transferphase. Then, the power reception apparatus 401 determines whether areception power reduction in the power reception apparatus 401 occursbased on the periodically measured reception power value. In a casewhere the calculated reception power value is smaller than a thresholdvalue or in a case where the difference between the calculated receptionpower value and the reference value is larger than a threshold value,the power reception apparatus 401 determines that a reception powerreduction in the power reception apparatus 401 occurs, and requests thepower transmission apparatus 402 to perform the foreign object detectionbased on the waveform attenuation method.

More specifically, the power reception apparatus 401 periodicallymeasures the reception power value and, according to the measurementresult, requests the power transmission apparatus 402 to perform theforeign object detection based on the waveform attenuation method withhigh accuracy of the foreign object detection. For example, in a casewhere the difference between the measured reception power and thereference value is equal to or less than a predetermined thresholdvalue, the power reception apparatus 401 may transmit the command forperforming the foreign object detection based on the Power Loss method.Meanwhile, in a case where the difference between the measured receptionpower and the reference value is larger than the predetermined thresholdvalue, the power reception apparatus 401 may transmit the command forperforming the foreign object detection based on the waveformattenuation method. In a case where a foreign object is highly likely toexist (in a case of the reception power reduction), the above-describedconfiguration enables performing the foreign object detection based onthe waveform attenuation method with high accuracy. Meanwhile, in a casewhere no foreign object is likely to exist, the above-describedconfiguration enables performing the foreign object detection based onthe Power Loss method while maintaining the high power transmissionefficiency.

In a case where the reduction in the reception power value is largerthan a threshold value, the power reception apparatus 401 determinesthat a foreign object exists and may request the power transmissionapparatus 402 to suspend the power transmission or reduce thetransmission power. For the reduction in the reception power value, thepower reception apparatus 401 may provide the first threshold value fordetermining that a foreign object is likely to exist and the secondthreshold value for determining that a foreign object exists. Then, in acase where the reception power reduction is larger than the firstthreshold value and is not larger than the second threshold value, thepower reception apparatus 401 requests the power transmission apparatus402 to perform the foreign object detection based on the waveformattenuation method. In a case where the reception power reduction islarger than the second threshold value, the power reception apparatus401 may transmit the EPT command to the power transmission apparatus 402to request the power transmission apparatus 402 to suspend the powertransmission. Alternatively, the power reception apparatus 401 maytransmit a command for requesting the power transmission apparatus 402to reduce the transmission power, to the power transmission apparatus402.

As described above, in a case where the power transmission apparatus 402and the power reception apparatus 401 detect the reception powerreduction in the power reception apparatus 401, the power transmissionapparatus 402 and the power reception apparatus 401 control theexecution of the foreign object detection based on the waveformattenuation method. This makes it possible to detect a foreign object inan early state in a case where a foreign object is likely to exist inthe vicinity of the power transmission apparatus 402 and the powerreception apparatus 401.

[Foreign Object Detection Processing According to Calibration Data]

Processing for the foreign object detection according to the dataobtained in the Calibration processing based on the Power Loss method orthe data obtained in the Calibration processing based on the waveformattenuation method will be described below.

As described above, in the foreign object detection based on the PowerLoss method and the foreign object detection based on the waveformattenuation method, the calibration processing is performed to set athreshold value as a reference that is used to determine presence orabsence of a foreign object. It is assumed that these pieces ofreference data obtained in the calibration processing indicate therelation between the transmission power value and the reception powervalue or between the transmission power value and the waveformattenuation factor in a state where no foreign object exists. Therefore,in a case where the reference data obtained in the calibrationprocessing does not indicate the predetermined relation between thetransmission power value and the reception power value or between thetransmission power value and the waveform attenuation factor, a foreignobject is likely to exist in the vicinity of the power transmissionapparatus 402 and the power reception apparatus 401. Therefore, thepower transmission apparatus 402 and the power reception apparatus 401control the execution of the foreign object detection.

Firstly, operations of the power transmission apparatus 402 and thepower reception apparatus 401 for performing the foreign objectdetection according to the data obtained in the calibration processingbased on the Power Loss method will be described below. The powertransmission apparatus 402 and the power reception apparatus 401 performthe calibration processing based on the Power Loss method, as processingfor determining the threshold value to be used for the Power Lossmethod. The data obtained in the calibration processing based on thePower Loss method represents the relation between the transmission powerand the reception power in a state where no foreign object exists, andthus possible range of the reception power value according to thetransmission power value can be estimated in advance. In a case wheredata is obtained in the calibration processing based on the Power Lossmethod, the power transmission apparatus 402 determines whether thereception power value included in the data falls within a rangepredetermined according to the transmission power value. In a case wherethe reception power value is out of the range, a foreign object islikely to exist in the vicinity of the power transmission apparatus 402and the power reception apparatus 401, and therefore the powertransmission apparatus 402 performs the foreign object detection basedon the waveform attenuation method. Then, in a case where the powertransmission apparatus 402 determines by the foreign object detectionbased on the waveform attenuation method that a foreign object exists,the power transmission apparatus 402 suspends the power transmission orreduces the transmission power. Meanwhile, in a case where the powertransmission apparatus 402 determines by the foreign object detectionbased on the waveform attenuation method that no foreign object exists,the power transmission apparatus 402 performs the calibration processingbased on the Power Loss method again to update the data.

More specifically, the power transmission apparatus 402 performs theforeign object detection based on the waveform attenuation method,different from the Power Loss method, according to the data valuesobtained in the calibration processing based on the Power Loss method.In a case where the power transmission apparatus 402 determines that aforeign object is likely to exist in the calibration processing based onthe Power Loss method, the above-described configuration enablesdetecting a foreign object in an early stage by performing the foreignobject detection based on the waveform attenuation method. Further, in acase where the accuracy of the foreign object detection based on thePower Loss method decreases because of incorrect calibration data, theuse of the waveform attenuation method enables detecting a foreignobject with high accuracy. The power reception apparatus 401 maydetermine whether a foreign object is detected according to the dataobtained in the calibration processing.

Operations of the power transmission apparatus 402 and the powerreception apparatus 401 in case of performing the foreign objectdetection according to the data obtained in the calibration processingbased on the waveform attenuation method will be described below. Thepower transmission apparatus 402 and the power reception apparatus 401perform the calibration processing based on the waveform attenuationmethod as processing for determining the threshold value to be used forthe waveform attenuation method. The reference data obtained in thecalibration processing based on the waveform attenuation method willrepresent the relation between the transmission power and the waveformattenuation factor in a state where no foreign object exists, and thusthe possible range of the data can be estimated in advance. The powertransmission apparatus 402 determines whether the waveform attenuationfactor indicated by the reference data obtained in the calibrationprocessing based on waveform attenuation method falls within apredetermined range. In a case where the waveform attenuation factor isout of the predetermined range, a foreign object is likely to exist inthe vicinity of the power transmission apparatus 402 and the powerreception apparatus 401, and therefore the power transmission apparatus402 performs the foreign object detection based on the Power Lossmethod. More specifically, the power transmission apparatus 402transmits a command for notifying the power reception apparatus 401 ofthe execution of the Power Loss method, to the power reception apparatus401. Upon reception of the command, the power reception apparatus 401transmits the command for performing the foreign object detection basedon the Power Loss method including the reception power value measured bythe power reception apparatus 401, to the power transmission apparatus402. Upon reception of the command from the power reception apparatus401, the power transmission apparatus 402 performs the foreign objectdetection based on the Power Loss method.

In a case where the power transmission apparatus 402 determines by theforeign object detection based on the Power Loss method that a foreignobject exists, the power transmission apparatus 402 performs control tosuspend the power transmission or reduce the transmission power.Meanwhile, in a case where the power transmission apparatus 402determines by the foreign object detection based on the Power Lossmethod that no foreign object exists, the power transmission apparatus402 performs the calibration processing based on the waveformattenuation method again to update the data. In this way, the powertransmission apparatus 402 performs the foreign object detection basedon the Power Loss method, different from the waveform attenuationmethod, according to the data value obtained in the calibrationprocessing based on the waveform attenuation method. In a case where thepower transmission apparatus 402 determines that a foreign object islikely to exist in the calibration processing based on the waveformattenuation method, the above-described configuration enables detectinga foreign object in an early stage by performing the foreign objectdetection based on the Power Loss method. The power reception apparatus401 may determine whether a foreign object is detected according to thedata obtained in the calibration processing.

[Foreign Object Detection Processing in Response to Temperature Rise]

Processing for the foreign object detection performed upon detection ofa temperature rise in the power transmission apparatus 402 or the powerreception apparatus 401 will be described below. Causes of temperaturerise in the power transmission apparatus 402 or the power receptionapparatus 401 include heat generation from electric circuits includingthe antennas of the power transmission apparatus 402 and the powerreception apparatus 401 and heat generation from the CPU that executesvarious processing. Also, in a case where a foreign object exists in thevicinity of the power transmission apparatus 402 and the power receptionapparatus 401, the foreign object consumes part of the energy of thetransmission power and generates heat. Accordingly, the powertransmission apparatus 402 or the power reception apparatus 401 incontact with the foreign object may also cause a temperature rise.Therefore, in a case where the temperature of the power transmissionapparatus 402 or the power reception apparatus 401 becomes higher than apredetermined threshold value, a foreign object is likely to exist inthe vicinity of the power transmission apparatus 402 and the powerreception apparatus 401. In this case, therefore, the power transmissionapparatus 402 and the power reception apparatus 401 control theexecution of the foreign object detection.

Operations performed by the power transmission apparatus 402 and thepower reception apparatus 401 in a case where the power transmissionapparatus 402 detects a temperature rise will be described below. Thepower transmission apparatus 402 includes a temperature sensor. In acase where the temperature sensor detects that the temperature of thepower transmission apparatus 402 is higher than a predeterminedthreshold value, the power transmission apparatus 402 performs theforeign object detection based on the waveform attenuation method. Then,in a case where the power transmission apparatus 402 determines that aforeign object exists, the power transmission apparatus 402 suspends thepower transmission or reduces the transmission power.

The reason why the power transmission apparatus 402 performs the foreignobject detection based on the waveform attenuation method, not based onthe Power Loss method, is as follows. In the Power Loss method, thepower transmission apparatus 402 needs to receive the reception powervalue from the power reception apparatus 401. In the waveformattenuation method, the power transmission apparatus 402 does not needinformation from the power reception apparatus 401, which makes itpossible to perform the foreign object detection in a shorter time. Inaddition, the foreign object detection based on the waveform attenuationmethod can perform the foreign object detection with higher accuracythan the Power Loss method. More specifically, in a case where atemperature rise occurs and a foreign object is likely to exist, thepower transmission apparatus 402 can achieve the high-accuracy foreignobject detection based on the waveform attenuation method in an earlystage. However, the power transmission apparatus 402 may perform theforeign object detection based on the Power Loss method. In this case,the power transmission apparatus 402 notifies the power receptionapparatus 401 that the foreign object detection based on the Power Lossmethod will be performed. Upon reception of the notification, the powerreception apparatus 401 transmits the command for performing the foreignobject detection based on the Power Loss method including the receptionpower value measured by the power reception apparatus 401, to the powertransmission apparatus 402.

Operations performed by the power transmission apparatus 402 and thepower reception apparatus 401 in a case where the power receptionapparatus 401 detected a temperature rise will be described below. Thepower reception apparatus 401 includes a temperature sensor. In a casewhere the temperature sensor detects that the temperature of the powerreception apparatus 401 is higher than a predetermined threshold value,the power reception apparatus 401 transmits the command for performingthe foreign object detection based on the waveform attenuation method,to the power transmission apparatus 402. Then, the power transmissionapparatus 402 performs the foreign object detection based on thewaveform attenuation method. In a case where the power transmissionapparatus 402 determines that a foreign object exists, the powertransmission apparatus 402 suspends the power transmission or reduce thetransmission power. The power transmission apparatus 402 may perform theforeign object detection based on the Power Loss method instead of thewaveform attenuation method. In this case, upon detection of temperatureinformation by the temperature sensor, the power reception apparatus 401transmits the command for performing the foreign object detection basedon the Power Loss method to the power transmission apparatus 402.

Predetermined rated values for allowable temperatures of powertransmission and power reception apparatuses may be prescribed instandards and laws of each country. Therefore, a threshold value fordetermining the execution of the above-described foreign objectdetection is set to a value lower than these rated values. Thus, even ina case where a temperature rise by a foreign object occurs, the foreignobject can be detected in an early stage before the temperature reachesa rated value.

[Foreign Object Detection Processing According to Transmission Power]

The foreign object detection processing performed based on the methodselected according to the transmission power transmitted from the powertransmission apparatus 402 will be described below. As described above,the foreign object detection based on the Power Loss method is performedbased on the loss of the transmission power during the powertransmission from the power transmission apparatus 402 to the powerreception apparatus 401. This method has a disadvantage that theaccuracy in the foreign object detection decreases while the powertransmission apparatus 402 is transmitting large power. On the otherhand, the method has an advantage that the high power transmissionefficiency can be maintained because the foreign object detection can beperformed while power is transmitted. The waveform attenuation methodhas another disadvantage that the power transmission efficiencydecreases when the power transmission is suspended. This is because themethod observes an attenuation factor of a transmission power waveformto perform the foreign object detection while the power transmissionapparatus 402 suspends the power transmission. On the other hand, themethod has another advantage that the foreign object detection can beperformed with high accuracy even during large power transmission.

Therefore, in a case where the transmission power value from the powertransmission apparatus 402 is less than a predetermined threshold value,the power transmission apparatus 402 and the power reception apparatus401 perform control to execute only the foreign object detection basedon the Power Loss method. This is because, in case of the lowtransmission power, even the foreign object detection based on the PowerLoss method provides high accuracy and hence the Power Loss methodmaintaining the high power transmission efficiency is advantageous.Meanwhile, in a case where the transmission power from the powertransmission apparatus 402 is equal to or larger than a predeterminedthreshold value, the power transmission apparatus 402 and the powerreception apparatus 401 performs control to execute the foreign objectdetection based on both the Power Loss method and the waveformattenuation method or execute only the foreign object detection based onthe waveform attenuation method. This is because, in case of the hightransmission power, the foreign object detection based on the Power Lossmethod provides the low accuracy of the foreign object detection andhence the foreign object detection based on the waveform attenuationmethod providing the high accuracy of the foreign object detection isadvantageous. Suitably using a plurality of foreign object detectionmethods according to the transmission power in this way enablesimproving the accuracy of the foreign object detection while maintainingthe high power transmission efficiency.

The foreign object detection processing in response to a communicationerror, the foreign object detection processing in response to the powerreduction, the foreign object detection processing according to thecalibration data, and the foreign object detection processing accordingto the temperature information have been described above centering on acase where both the Power Loss method and the waveform attenuationmethods are used. However, in a case where the transmission power islower than a predetermined threshold value, in these exemplaryembodiments, the foreign object detection based on the Power Loss methodmay be performed at the timing when the foreign object detection basedon the waveform attenuation method is performed. In a case where thetransmission power is equal to or larger than a predetermined thresholdvalue, the exemplary embodiments may use both the Power Loss method andthe waveform attenuation methods or perform the foreign object detectionbased on waveform attenuation method at the timing when the foreignobject detection based on the Power Loss method is performed.

The present exemplary embodiment has been described above centering on acase where the wireless power transmission system determines whether apredetermined condition related to a state of at least either one of thepower transmission apparatus 402 and the power reception apparatus 401is satisfied, and, according to the determination result, selectivelyuses the Power Loss method and the waveform attenuation method. However,the present invention is not limited thereto. At least either one of thepower transmission apparatus 402 and the power reception apparatus 401may suitably use a plurality of foreign object detection methodsincluding foreign object detection methods other than the aboveaccording to a condition. The wireless power transmission system maycontrol the selection of foreign object detection methods and theexecution of the foreign object detection processing through thecombination of a plurality of conditions including the above-describedvarious conditions and other conditions.

According to various embodiments of the present disclosure, it ispossible to suitably control the detection processing in a case where aplurality of detection methods for detecting an object different fromthe power reception apparatus is available in performing the wirelesspower transmission.

Other Embodiments

Embodiment(s) of the present disclosure can also be realized by acomputer of a system or apparatus that reads out and executes computerexecutable instructions (e.g., one or more programs) recorded on astorage medium (which may also be referred to more fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment(s) and/or controlling the one or more circuits to perform thefunctions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., central processingunit (CPU), micro processing unit (MPU)) and may include a network ofseparate computers or separate processors to read out and execute thecomputer executable instructions. The computer executable instructionsmay be provided to the computer, for example, from a network or thestorage medium. The storage medium may include, for example, one or moreof a hard disk, a random-access memory (RAM), a read only memory (ROM),a storage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

While various embodiments of the present disclosure have been describedwith reference to exemplary embodiments, it is to be understood that theinvention is not limited to the disclosed exemplary embodiments. Thescope of the following claims is to be accorded the broadestinterpretation so as to encompass all such modifications and equivalentstructures and functions.

What is claimed is:
 1. A power transmission apparatus comprising: apower transmission unit configured to wirelessly transmit power to apower reception apparatus; a first detection unit configured to performdetection processing using a first detection method for detecting anobject different from the power reception apparatus based on a powerloss related to a power transmission by the power transmission unit; adetermination unit configured to determine whether a predeterminedcondition related to a state of at least either one of the powerreception apparatus and the power transmission apparatus is satisfied;and a second detection unit configured to perform detection processingusing a second detection method for detecting an object different fromthe power reception apparatus based on at least either one of a voltageattenuation state and a current attenuation state related to the powertransmission by the power transmission unit, according to thedetermination result by the determination unit.